Ecob01

I also had that same problem, started around 72,000 got progressively worse. the dealer couldn't find the reason so I had him change the plugs and it FIXED it ran like new again. it restarted doing it again at 130,000 miles so I changed the plugs and again runs like new. The new type plugs don't last as long. I found very tiny hair line cracks in 2 of the ones I took out.
but for some reason the new plug don't throw trouble codes like the old ones would when the start messing up. so change them out it is easy and cheap

Mif

Did my plugs this weekend. None were showing cracks, but I went ahead with brand new SP-534's. It may have smoothed out a bit of my rough idle, but I am still getting my vibration around 21-22 MPH.

acdii

Does it continue to vibrate up to 55? or just vibrates at 21-22 and smooths out? The Engine misfire from the plugs happens under load when under the boost threshold, or when under at or near WOT with boost. Sounds more like a driveline issue with yours than with the engine. Something is out of balance.

Ecob01

2011
3.5 Ecoboost supper crew
145" wheel base
4x4 XLT
Camano WA.
10/2011

Joseph Schaffer

2012
3.7 Flex Fuel
145"
4X2 XLT
Ontario
05/2012

beselby

Okay, shudder never left after changing plugs. Still feels like hitting a potholes at 1500 rpms in 5th and 6th. Another F150 owner said he had same problem so he flushed his transmission and gave me the name of a good place to have this done. I called them. They told me not to flush the trans but maybe drain and change the fluid. He also asked if I changed the coil packs when plugs were changed. I didn't. Ford dealer never asked so I didn't. Could coil packs make the difference here?

notben

2012
3.5 Ecoboost supper crew
145" wheel base
4x4 Lariat
Dearborn
04/12

EDDLG01

I had the truck for 3 months and I replace the tires, I notice a little vibration around 55 MPH and had the tire shop rebalance the tires after I had 1000 miles on them, it didn't change anything, I also had the spark plugs replace and still doing the same thing, my truck production date is 11/10, 2011 XLT Super Cab 145" wheel base with the 5.0 engine, it looks like my truck doesn't qualified for the RECALL, what can I do about that vibration on 55MPH...
Can some one give me heads up on my issue...
THANKS

winchested

You can drive it ans set your cruise at 57 mph!

Erock67

My 2011 scab xl 3.7 2wd definitely gets the bed shimmy at 55 mph. I usually just accelerate to around 60 and it settles down. At 55, you can look in the side mirror and see that the bed is shaking. I know it's not the road because they just repaved a 10 mile stretch of the road I take to work.

Must be a harmonics issue with the rolling chassis and body since it seems to affect all engine and body types. I've noticed the passenger seat gets the shakes at times also.

Outside of the 55-60 shake, the truck runs smooth.